Hydroxycitrate

Hydroxycitrate is a slight variation of a common acid (citric acid) commonly found in fruits, and hydroxycitrate (because of its close similarity to citric acid) has strong effects on the metabolism that bias the body towards burning fat and decrease appetite. Citric acid (or to be slightly more accurate, citrate) is involved in the Krebs cycle, the master cycle that forms the foundation of both the burning of food for energy and the production of various biological molecules.
Hydroxycitrate works by inhibiting the enzyme acetyl coenzyme A lyase, which produces substances that in turn go on to produce various fats - including normal fats, the ones that slimmers are trying to avoid accumulating, and also cholesterol.
Hydroxycitrate also reduces appetite, because of this inhibition. The biochemicals that cannot be made into fats have to go somewhere - and they go on to produce higher levels of glycogen, the form in which carbohydrate is stored in the body.
Hydroxycitrate therefore, at one and the same time, reduces conversion of excess calories into fat and also reduces appetite, which in turn reduces the amount of excess calories to be so converted.
Hydroxycitrate is found in relatively large amounts in Garcinia cambogia (Malabar tamarind) which has been used for thousands of years to make meals more "filling". In fact, Garcinia cambogia is the plant from which hydroxycitrate is commercially extracted and made into supplements.
People recommending hydroxycitrate do not have to rely on theory - it has been clinically trialled several times, and has been tested extensively on various animals - none of the animals were harmed in the testing, and in fact there was no reason to expect them to be harmed, because as previously stated hydroxycitrate, in the form of the fruit it comes from, has been used for millennia with no ill effects to the people eating it.
Hydroxycitrate is therefore a very valuable additional aid to any weight loss or control programme.